Motor vehicle powertrains typically include a transmission interposed between the engine and the differential providing torque to the vehicle's driven wheels. Transmissions provide a manual or automated selection of speed ratios between the speed of rotation of the transmission input shaft and the rotation speed of the output shaft resulting in output torque multiplication or reduction with the goal of matching vehicle on-ground torque and speed demands to the engine's output speed and torque capabilities while maintaining engine operating parameters within optimum fuel efficiency and emission ranges.
A variety of different types of transmissions are used to deliver multiple speed ratios including manual, automated manual, dual clutch, continuously variable transmissions and various types of planetary transmissions. One example type of transmission is a dual clutch transmission which utilizes two friction clutches along with dog clutches and synchronizers to achieve dynamic speed and torque ratio shifts by alternating between one friction clutch and the other and several dog clutch/synchronizers where the synchronizers are preset for the oncoming ratio to actually make the dynamic speed/torque ratio shift.
Early motor vehicle transmissions typically provided two, three or maybe four forward speed ranges. In the interest of increasing fuel economy the number of forward speed ranges has tended to increase in recent years with the advantage of permitting the engine to operate within a desired fuel efficient optimum engine speed and torque range relatively independent of vehicle ground speed conditions.
Vehicle fuel economy and production/retail cost is further impacted by vehicle parts complexity and component weight/material considerations, including transmission parts complexity, size and weight.